This application is submitted to NIDA in response to PA-03-126, Behavioral Therapies Development Program, and proposes a Stage lb efficacy trial of a medical office brief intervention for adolescent drug abuse. Use of drugs is associated with a variety of health care problems, making settings where adolescents receive routine medical care ideal for implementation of routine screening and early intervention. However, medical settings are currently underutilized in this regard and new evidence-based strategies are needed to improve practice patterns, including standardized methods of screening, assessment, intervention, and referral to treatment. This investigative team has previously conducted studies aimed at assessing the reliability of substance abuse screening tests among adolescent medical patients. We then developed a new brief screen, the CRAFFT, which is both developmentally appropriate for adolescents and practical for use in busy clinic settings. We also completed a Stage 1a feasibility study of a medical office-based brief intervention based on motivational interviewing. Preliminary results from the Stage 1a study suggest that our approach will be effective in reducing use of drugs among 12-18 year old adolescent medical patients. We have developed a draft therapy manual, clinical encounter forms, a clinician training protocol, and a measurement battery. We are now prepared to conduct a Stage 1b study of the new intervention, which will use a randomized controlled design. The specific aims of the proposed plan are to: (1) Test the effect of the brief intervention on drug use, (2) Test the effect of the brief intervention on engagement in treatment, (3) Test the effect of the brief intervention on other substance-related outcomes, and (4) Identify factors that moderate and/or mediate the effect of the intervention on outcomes of interest and estimate their effect sizes. An effective brief intervention for drug abuse could be widely implemented in settings where adolescents receive routine healthcare, and would be of enormous public health significance across the U.S.